PIC16F1825T-ESS datasheet(150/448 Pages) MICROCHIP

150 / 448 page

PIC16(L)F1825/1829

DS41440C-page 150

 2010-2012 Microchip Technology Inc.

16.1

ADC Configuration

When configuring and using the ADC the following

functions must be considered:

• Port configuration

• Channel selection

• ADC voltage reference selection

• ADC conversion clock source

• Interrupt control

• Result formatting

16.1.1

PORT CONFIGURATION

The ADC can be used to convert both analog and

digital signals. When converting analog signals, the I/O

pin should be configured for analog by setting the

associated

TRIS

and

ANSEL

bits.

Refer

Section 12.0 “I/O Ports”

for more information.

16.1.2

CHANNEL SELECTION

There are up to 15 channel selections available:

• AN<7:0> pins (PIC16(L)F1825 only)

• AN<11:0> pins (PIC16(L)F1829 only)

• Temperature Indicator

• DAC_output

•FVR Buffer1

Refer to Section 17.0 “Digital-to-Analog Converter

(DAC) Module”

, Section 14.0 “Fixed Voltage Refer-

ence (FVR)”

and Section 15.0 “Temperature Indicator

Module”

for more information on these channel

selections.

The CHS bits of the ADCON0 register determine which

channel is connected to the sample and hold circuit.

When changing channels, a delay is required before

starting the next conversion. Refer to Section 16.2

“ADC Operation”

for more information.

16.1.3

ADC VOLTAGE REFERENCE

The ADPREF bits of the ADCON1 register provides

control of the positive voltage reference. The positive

voltage reference can be:

•VREF+ pin

•VDD

• FVR 2.048V

• FVR 4.096V (Not available on LF devices)

The ADNREF bits of the ADCON1 register provides

control of the negative voltage reference. The negative

voltage reference can be:

•VREF- pin

•VSS

See Section 14.0 “Fixed Voltage Reference (FVR)”

for more details on the Fixed Voltage Reference.

16.1.4

CONVERSION CLOCK

The source of the conversion clock is software

selectable via the ADCS bits of the ADCON1 register.

There are seven possible clock options:

•FOSC/2

•FOSC/4

•FOSC/8

•FOSC/16

•FOSC/32

•FOSC/64

•FRC (dedicated internal oscillator)

The time to complete one bit conversion is defined as

TAD. One full 10-bit conversion requires 11.5 TAD

periods as shown in Figure 16-2.

For correct conversion, the appropriate TAD specification

must be met. Refer to the A/D conversion requirements

in Section 30.0 “Electrical Specifications” for more

information. Table 16-1 gives examples of appropriate

ADC clock selections.

Note:

Analog voltages on any pin that is defined

as a digital input may cause the input

buffer to conduct excess current.

Note:

Unless using the FRC, any changes in the

system clock frequency will change the

ADC

clock

frequency,

which

may

adversely affect the ADC result.

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